1. Field of the Invention
The present invention relates to a hydraulic motor unit that includes a hydraulic motor and a volume adjusting mechanism for changing a volume of the hydraulic motor.
The present invention also relates to a hydraulic four-wheel-drive working vehicle that includes first and second wheels disposed on one side and the other side in a vehicle longitudinal direction, respectively, in such a manner as that the first wheels have a turning radius smaller than that of the second wheels; a variable-displacement type hydraulic motor unit operatively driving the first wheels; a fixed-displacement type hydraulic motor unit operatively driving the second wheels; and one or plurality of hydraulic pump unit, wherein the variable-displacement type hydraulic motor unit and the fixed-displacement-type hydraulic motor unit are fluidly driven by the hydraulic pump unit in a synchronized manner to each other.
2. Related Art
A variable-displacement-type hydraulic motor unit including a hydraulic motor and a volume adjusting mechanism for changing a volume of the hydraulic motor is used in hydraulic four-wheel-drive working vehicle or the like.
For example, U.S. Pat. No. 6,889,793 (hereinafter, referred to as prior art document 1) discloses an articulate-type working vehicle with a variable-displacement-type hydraulic motor unit functioning as a hydraulic motor unit that operatively drives one of front and rear wheels.
More specifically, in an articulate-type working vehicle that includes front and rear frames disposed on front and rear sides, respectively, and connected to each other in a state that they could swing to each other around a pivot shaft along a substantially vertical direction; front and rear wheels supported by the front and rear frames, respectively; a front hydraulic motor unit operatively driving the front wheels; a rear hydraulic motor unit operatively driving the rear wheels; a hydraulic pump unit fluidly connected in series to the front and rear hydraulic motor units; wherein a length in a vehicle lengthwise direction between the rear wheels and the pivot shaft is shorter than that between the front wheels and the pivot shaft, there is caused a difference in turning radius between the front wheels and the rear wheels in accordance with a turning angle of the vehicle.
In order to compensate for the difference in turning radius, the articulate-type working vehicle includes the variable-displacement-type hydraulic motor unit as one of the front and rear hydraulic motor units.
The variable-displacement-type hydraulic motor unit includes a hydraulic motor and a volume adjusting mechanism that changes a volume of the hydraulic motor. The working vehicle is configured so as to increase or reduce the volume of the hydraulic motor by operating the volume adjusting mechanism in accordance with the turning angle of the vehicle, thereby increasing or reducing driving speed of the corresponding wheels out of the front and rear wheels in accordance with the difference in turning radius between the front wheels and the rear wheels.
However, the variable-displacement-type hydraulic motor unit disclosed by the prior art document 1 is configured so that the volume adjusting mechanism is mechanically operated. As a result, there is needed a structure for transmitting to the volume adjusting mechanism a mechanical movement in accordance with turning motion of the vehicle.